The brace stretching around the car laterally will, in theory, increase the rigidity of the chassis. The E82 has such a stiff chassis already, the affect will be minimal. I added one to my car and there was no discernible difference. I'd spend my money on a sway bar instead.

i personally find the chassis to be a bit too floppy for my liking - definitely not as rigid as my previous (modified) cars

Agreed. Coming from an E46 M3 and E85 Z4M, the 135i's chassis leaves A LOT to be desired in terms of stiffness. Even getting a dealer's E90 loaner several times was an improvement over the sloppy feel of my 135i. Upgrading to M3 suspensions bits has since improved the overall chassis feel for me, but it's still a far cry from what I'm used to.

i personally find the chassis to be a bit too floppy for my liking - definitely not as rigid as my previous (modified) cars

Agreed. Coming from an E46 M3 and E85 Z4M, the 135i's chassis leaves A LOT to be desired in terms of stiffness. Even getting a dealer's E90 loaner several times was an improvement over the sloppy feel of my 135i. Upgrading to M3 suspensions bits has since improved the overall chassis feel for me, but it's still a far cry from what I'm used to.

You can get front + rear strut tower bars, underbody front (2 point at least) - and i haven't looked but i'd say also front L+R under-fender braces

I wouldn't call it outright *floppy* - tests show that it's a pretty good and stiff chassis compared to most stock cars.. But again, i'm used to 'floppy' oem cars that have a whole bunch of bracing to pretty much make them as stiff as possible (without fully custom seam welding etc.) - after riding in a few cheaper cars with bracing, then my car.. It's not much to fix up, and what stiffening can be done is more than sufficient

M3's and z4's also have very stiff and low suspension, more seam welds, thicker sway bars (and more solid strut braces from the factory)

Certain strut hat mounts and/or camber plates don't fit with stock strut braces, they however fit with M3 strut braces. Just throwing that out there when considering to upgrade your front strut support setup. Best would be as mentioned above, a 3 point system, pretty much a triangle on your engine bay.

A brace designed to tie the firewall and the towers together will give you better rigidity then just a brace mounted between the two towers. The M3 style brace also spreads the load evenly over the tower, not just to one point only.

A brace designed to tie the firewall and the towers together will give you better rigidity then just a brace mounted between the two towers. The M3 style brace also spreads the load evenly over the tower, not just to one point only.

But wouldn't the firewall only one not share the load properly, since the towers aren't actually linked, just stiffened?